Minimizing particle contamination of semiconductor wafers during pressure evacuation by selective orientation and shielding

ABSTRACT

A method including placing a wafer active side down in a chamber and reducing the pressure in the chamber. An apparatus or system including a chamber having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a vacuum; and a support to maintain a wafer in the volume of the chamber with minimum or no contact with an active side of the wafer, wherein an amount of particles that an active side of a wafer is exposed to during a pressure change in the chamber is minimized when the wafer is loaded in the chamber in an active side down configuration.

BACKGROUND FIELD

Semiconductor processing.

BACKGROUND

In the field of semiconductor processing, particularly, at the waferlevel, semiconductor substrates (e.g., wafers) are subject to a numberof processing operations in one or more processing chambers. Oneprocessing environment is a under vacuum condition. To bring a conditionto a vacuum, a substrate, such as a wafer, is generally placed in achamber and the chamber evacuated to bring the pressure to a vacuum.Often times, the vacuum processing is a multi-chamber operation in whicha substrate is placed in a first chamber or load lock. The first chamberor load lock is connected to a second chamber (processing chamber) wheremodifications to the substrate are made. Utilizing a load lock meansthat a wafer can be loaded into a processing chamber without having topump-down the processing chamber again. One reason for utilizing theload lock is that a subsequent pumping down to a pressure required in aprocessing chamber tends to introduce contaminants as particles can geton the substrate during the pump-down. Accordingly, a substrate isloaded in a load lock which is then pumped down to the desired pressureof the processing chamber. After the load lock opens, the substrate ismoved into the processing chamber.

Currently, substrates (e.g., wafers) are predominantly in an active sideup orientation while pump-down and purging/venting is done. By activeside up orientation is meant that a side of a wafer having eitherdevices formed therein/thereon or intended to have devices formedtherein/thereon faces a direction opposite the direction of gravity. Inthis state, the gravitational forces within the chamber act to pullparticles onto an active surface of the substrate particularly duringpump down.

Particle contamination in reduced pressure chambers, such as in a vacuumload lock environment may be a significant source of defects. Theseparticles come from the chamber material itself, from handlingoperations, from previous operations in the chamber, etc. It isappreciated that contaminating particles have a varied sizedistribution. The number of small particles (e.g., sub-micron sizedparticles) far exceeds the number of larger particles. As criticaldensities increase on wafers, the contribution of smaller particles toparticle contamination increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of embodiments will become morethoroughly apparent from the following detailed description, appendedclaims, and accompanying drawings in which:

FIG. 1 shows a schematic process sequence of loading a wafer into a loadlock.

FIG. 2 shows a wafer in a load lock chamber and illustrates a purgeprocess.

FIG. 3 shows the load lock of FIG. 2 during a pump down process.

FIG. 4 shows the load lock of FIG. 3 at a process pressure.

FIG. 5 shows the wafer of FIG. 4 being loaded from a load lock into aprocessing chamber at a desired pressure.

FIG. 6 shows a schematic top view of a wafer supported in an active sidedown configuration with a support serving also as a particle deflectionplate.

FIG. 7 shows a schematic top view of a wafer supported in an active sidedown configuration by a support with a particle deflection plate betweenthe support and the wafer.

FIG. 8 shows a schematic top side view of a wafer supported by anelectrostatic charge in an active side down configuration with aparticle deflection place beneath the wafer.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates the loading of a substrate (e.g.,wafer) into a load lock. Referring to FIG. 1, load lock 100 includeschamber 110 that is, for example, a metal (e.g., aluminum) materialhaving a volume 105 that is capable of maintaining a reduced pressureenvironment, including a vacuum or zero pounds per square inch (psi).Volume 105 is also sized to accommodate at least one wafer (e.g., a 200millimeters (mm) or 300 mm wafer) therein. Chamber 110 includes exhaustport 120 that may be used to evacuate chamber 110. Also connected tochamber 110 is pressure sensor 130 such as Baratrome pressure sensor. Apressure indication of pressure sensor 130 may be read by processor 140.Processor 140, in one example, includes machine-readable programinstructions to record pressure measurements of volume 105, and toperform a method to evacuate chamber through exhaust port 120 to apredetermined pressure. Chamber 110 also includes gas entry port 155 tointroduce a gaseous species into volume 105. In the embodiment shown inFIG. 1, purge gas 150 is connected to entry port 155. Gas source 150 is,for example, a purge gas, such as nitrogen (N₂). Introduction of a gasthrough gas source 150 is regulated by valve 160. Valve 160 iscontrolled, in this example, by processor 140 and machine-readableinstructions therein (e.g., instructions to perform a method to purgechamber 110).

FIG. 1 also shows arm 175 such as a robotic arm, holding wafer 170. Inan initial holding phase, wafer 170 includes active side 180 facing, asviewed, upward or against gravity. In one embodiment, arm 175 may beactuated to rotate so that active side 180 of wafer 170 is directed atgravity (e.g., rotated 180 degrees downward as viewed). Arm 175 maymaintain wafer 170 in an active side down (with gravity) configurationby, for example, side clamping, electrostatic forces or a vacuum orsimilar reduced pressure on a back side of wafer 170. Arm 175 may beadvanced to introduce wafer 170 into chamber 110 in an active side downconfiguration and retracted to be free from the chamber.Machine-readable program instructions in processor 140 or a separateprocessor may be used to control among other functions the securing ofwafer 170 by arm 175, the rotation of arm 175, and the placement ofwafer 170 into chamber 110.

Referring again to the contents of volume 105 of chamber 110, volume 105also includes, in one embodiment, particle displacement plate 190. Inone embodiment, particle displacement plate 190 has a diameter that isequal to or slightly less than a diameter of wafer 170. By slightlyless, it is meant, in one embodiment, but not necessarily limited to,one millimeter to three millimeters less in diameter (e.g., 5-7 mm for a200 mm wafer or 9-11 mm for a 300 mm wafer). In the embodiment shown,particle displacement plate 190 is supported by stage 195 that may bemoved up or down (as viewed) within chamber 105 such movement optionallycontrolled by program instructions in processor 140 or anotherprocessor. In one embodiment, particle displacement plate 190 isadvanced to a position, in one embodiment, within a few millimeters(e.g., 1-4 mm) from active side 180 of wafer 170.

FIGS. 2-4 illustrate a series of processing operations within chamber110 of load lock 100. Referring to FIG. 2, wafer 170 is placed inchamber 110, volume 105 of chamber 110 is sealed and purge gas 210 isintroduced. In one embodiment, purge gas 210 is a nitrogen gas.

FIG. 3 shows chamber 110 during a pump-down operation. In oneembodiment, volume 105 of chamber 110 is reduced in pressure (pumpeddown) to a vacuum condition. Referring to FIG. 1, pressure sensor 130may be used to monitor the pressure in chamber 110 and exhaust port 120may be used to evacuate chamber 110. With wafer 170 in an active sidedown (with gravity) position, the pump down process occurs in such a wayto allow gravitational force to act against particles moving towardswafer 170. Particle displacement plate 190 inhibits particles frombouncing towards active side 180 of wafer 170. As the pressure dropsduring a pump down process, a Stokes drag experienced by particles 310decreases significantly. If particles 310 achieve ballistic velocities,the particles can suffer multiple collisions with chamber 110 and othersurfaces and ultimately end up on active side 180 of wafer 170. Particledisplacement plate 190 inhibits the possibility of colliding particlesending up on active side 180.

FIG. 4 shows chamber 110 following the pump down process. In FIG. 4, thepressure in volume 105 of chamber 110 is selected to be, in oneembodiment, equivalent to a pressure in a processing chamber where wafer170 will be transferred. The number of unwanted particles on active side180 of wafer 170 have been reduced due to the configuration of wafer 170in chamber 110 and, in this embodiment, the presence of particledisplacement plate 190.

FIG. 5 shows wafer 170 transferred from chamber 110 to processingchamber 510. In one embodiment, chamber 110 is connected to processingchamber 510 through entry port 520 that may be sealed while chamber 110is undergoing a pump down process. In one embodiment, a volume ofchamber 510 has been pumped down to a pressure equivalent to the pumpeddown pressure of volume 105 of chamber 110. Wafer 170 may be transferredto chamber 510 in an active side up or active side down configurationdepending on the desired processing environment. In chamber 510, one ormore semiconductor processing operations may be performed on wafer 170.Representative processing operations that may be performed under vacuumconditions include implant, etch, extreme ultraviolet lithography, andmasked-beam processing. Following processing, wafer 170 may optionallybe returned to chamber 110 in an active side down configuration andpurging operations may be performed. In this manner, after processingthe potential of particle contaminants contacting active side 180 ofwafer 170 may be reduced.

FIGS. 6-8 show various ways to support a wafer within a chamber, such asa load lock, during a pump down process. Each embodiment shows a waferin an active side down (in a direction with gravity) configuration. FIG.6 shows wafer 670 supported by support 690. In this embodiment, support690 serves as a support and as a particle displacement plate. Wafer 670is supported by support 690 in an active edge grip support configurationwith vertical supports 695 (e.g., a few millimeters in length)supporting wafer 670 outside an active area (e.g., at several pointsalong an edge of wafer 670). FIG. 7 shows a second embodiment wherewafer 770 is supported in an active edge grip configuration by support775 with vertical supports 795. Particle displacement plate 790 isplaced on support 775 (and supported by vertical supports 777) and, inone embodiment, has a diameter smaller than support 775. In oneembodiment, support 775 has a diameter equal to or greater than adiameter of wafer 770.

FIG. 8 shows a third embodiment where wafer 870 is chucked by chuck 875.A passive side of wafer 870 is supported by chuck 875 through, forexample, electrostatic forces. In this embodiment, particle displacementplate 890 is not in contact with an active side of wafer 870.

In the preceding detailed description, reference is made to specificembodiments thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense.

1. A method comprising: placing a wafer active side down in a chamber;and reducing the pressure in the chamber.
 2. The method of claim 1,wherein reducing the pressure comprises reducing the pressure from afirst pressure to a vacuum.
 3. The method of claim 1, wherein thechamber is a first chamber, the method further comprising: afterreducing the pressure in the first chamber, transferring the wafer to asecond chamber.
 4. The method of claim 3, further comprising modifyingthe active side of the wafer in the second chamber.
 5. The method ofclaim 4, wherein modifying comprises an extreme ultraviolet lightpatterning technique.
 6. The method of claim 4, further comprising,after modifying, transferring the wafer from the second chamber to thefirst chamber.
 7. An apparatus comprising: a chamber having an interiorvolume suitable to accommodate a semiconductor wafer and capable ofmaintaining a vacuum; and a support to maintain a wafer in the volume ofthe chamber with minimum or no contact with an active side of the wafer,wherein an amount of particles that an active side of a wafer is exposedto during a pressure change in the chamber is minimized when the waferis loaded in the chamber in an active side down configuration.
 8. Theapparatus of claim 7, further comprising a plate disposed beneath anactive side of a wafer when the wafer is loaded in the chamber in anactive side down configuration.
 9. The apparatus of claim 8, wherein theplate comprises the support.
 10. The apparatus of claim 8, wherein theplate is disposed between the support and an active side of a wafer whena wafer is loaded in the chamber in an active side down configuration.11. The apparatus of claim 8, wherein the plate has a dimension similarto a dimension of an active side of a wafer.
 12. The apparatus of claim7, wherein the chamber is a first chamber adapted to be coupled to asecond chamber such that a pressure in the first chamber can bemaintained on a transfer of a wafer from the first chamber to the secondchamber.
 13. A system comprising: a first chamber having an interiorvolume suitable to accommodate a semiconductor wafer and capable ofmaintaining a vacuum, the first chamber comprising: a support tomaintain a wafer in the volume of the chamber with minimum or no contactwith an active side of the wafer; a plate disposed between and a wall ofthe chamber and an active side of a wafer when the wafer is loaded inthe chamber in an active side down configuration; and a second chambercoupled to the first chamber and having an interior volume suitable toaccommodate a semiconductor wafer and capable of maintaining a pressureestablished in the first chamber on transfer of a wafer from the firstchamber to the second chamber, wherein the second chamber is capable ofperforming an operation to modify an active site of a wafer.
 14. Thesystem of claim 13, wherein the plate comprises the support.
 15. Thesystem of claim 13, wherein the plate has a dimension similar to adimension of an active side of a wafer.
 16. The system of claim 13,wherein the plate has a diameter less than a diameter of a wafer withinthe volume of the first chamber.